Abstract Ovarian carcinoma remains the cancer with the highest mortality rate among gynecological tumors. Although many ovarian cancer patients fully respond to the standard combination of surgery and chemotherapy, nearly 90% later develop recurrent chemotherapy-resistant cancer and inevitably succumb to their disease. Thus, development of innovative, effective therapies against recurrent/chemotherapy-resistant ovarian cancer remains a high priority for improving public health. Using high-throughput technologies to analyze genetic fingerprints of ovarian cancer, we have recently discovered extremely high expression of the genes encoding the proteins claudin-3 and claudin-4. Because claudin-3 and -4 are the epithelial receptors for Clostridium perfringens enterotoxin (CPE), and are sufficient to mediate CPE binding, we hypothesize that using biodegradable nanoparticles such as poly(lactic-co-glycolic acid, i.e., PLGA-NP) encapsulating therapeutic agents complexed to the binding domain of CPE, to target ovarian cancer cells, is a novel, potentially highly effective therapeutic approach to treat chemotherapy-resistant ovarian cancer. Consistent with this view, preliminary in vitro data clearly showed that fluorescein(FITC)-labeled-C-CPE effectively binds and rapidly internalizes in chemotherapy-resistant primary OSPC cell lines, suggesting that C- CPE is capable to bind and also of translocating drugs across cell tumor membrane. More importantly, preliminary in vivo results showed that CPE-PLGA-NP encapsulating a fluorescent dye (coumarin) selectively accumulate in vivo in chemotherapy resistant ovarian tumors with minimal nonspecific accumulation in RES organs and only background binding in normal cells of various other organs. Accordingly, this proposal has three related specific aims: 1) Characterize fluorescent PLGA-NP encapsulating model and therapeutic drugs, complexed to CPE peptides of different lengths (i.e., 30aa, 17aa and 9 aa), and evaluate binding activity and therapeutic efficacy of such NP in multiple in vitro assays against primary chemotherapy resistant ovarian carcinoma cell lines, 2) Examine the distribution and pharmacokinetics of PLGA-NP encapsulating coumarin complexed to 125I labeled C-CPE peptide in vivo in clinically relevant animal models of primary chemotherapy resistant ovarian carcinoma and 3) Examine the therapeutic potential of PLGA-NP encapsulating plasmid DNA encoding Diptheria Toxin A suicide protein under the control of promoter sequences of genes highly and preferentially active in ovarian cancer (i.e., mesothelin and HE4/WFDC2), complexed to CPE peptide in vivo in clinically relevant animal models of primary chemotherapy resistant ovarian carcinoma. Upon completion of this project, we will be positioned to quickly translate this research into a novel, highly effective therapeutic treatment for patients with chemotherapy-resistant disease.